Skip to main content

Requirements Confusion

Over on Seilevel's Requirements Defined message board, Joy Beatty wrote about her recent experience at a requirements conference:

I heard some new ideas about NFRs [nonfunctional requirements] - One was that the distinguisher is that FRs [functional requirements] are quantifiable and NFRs are not. I'm not sure that I think any requirement is not quantifiable if you try hard enough to make it so.

A further explained response was that using “testable” as a distinguisher, meant that the requirement can be tested by execution of the system (FR = function or performance) vs something you might test about the environment of the system (NFR = maintainability).
In my opinion, these anecdotes only underscore just how misunderstood requirements are. People at a requirements conference were saying these things? Wow.

As I've mentioned, a nonfunctional requirement is just as testable and quantifiable as a functional requirement.

Functional requirements state what the system should do. The system either does it or doesn't do it. So sure, functional requirements are testable.

Nonfunctional requirements are simply metrics that we attach to functional requirements. While the system is doing whatever it's supposed to be doing, we can measure things like throughput (performance), how long it takes for a typical user to accomplish her goals (usability), the percentage of time the system is available to deliver any particular functionality (availability), etc. These nonfunctional requirements are by their very nature testable (at least in principle) and quantifiable.

Comments

Kevin Brennan said…
Absolutely. I'm not sure there is such a thing as a non-testable requirement; if you can't define a way to test it how can you state whether or not it has been met?

A non-testable requirement might be more accurately described as a goal.

Quantifiable is also not a good description--I can easily think of functional requirements that aren't quantifiable.
Joy said…
Roger, I'm with you on this, I was just quoting what I heard. I can't comprehend writing a requirement that you cannot measure.

Though I will slightly argue with Kevin's comment that quantifiable may actually not be an ok term - it may just be semantics though. But, right or wrong, I equated in my mind that "quantifiable" is the same as "measurable".
Kevin Brennan said…
Hi Joy,

Is a requirement like "the user interface will be available in English, French, and Spanish" quantifiable, in the way you use the term? (It's certainly testable). I don't think of it that way, but if you do then our disagreement is probably just semantic.

Popular posts from this blog

Why Spreadsheets Suck for Prioritizing

The Goal As a company executive, you want confidence that your product team (which includes all the people, from all departments, responsible for product success) has a sound basis for deciding which items are on the product roadmap. You also want confidence the team is prioritizing the items in a smart way. What Should We Prioritize? The items the team prioritizes could be features, user stories, epics, market problems, themes, or experiments. Melissa Perri  makes an excellent case for a " problem roadmap ", and, in general, I recommend focusing on the latter types of items. However, the topic of what types of items you should prioritize - and in what situations - is interesting and important but beyond the scope of this blog entry. A Sad but Familiar Story If there is significant controversy about priorities, then almost inevitably, a product manager or other member of the team decides to put together The Spreadsheet. I've done it. Some of the mos

What Product Managers Can Learn from the Apple iPod

The Story When Apple unveiled its iPod digital music player back in October 2001, I dismissed it as a  parity product . I already owned the Cowon iAUDIO CW100 MP3 player, loaded with my favorite tunes. There was Apple, generating great hype over the iPod as if it were a breakthrough product. The idea of a portable digital music player was nothing new. The first mass-produced MP3 players came out in 1998. In late 2001, the concept may have been new to a lot of Apple customers, but it wasn't new to me. I proudly showed my MP3 player to friends when they gushed about the iPod. Thus Apple's iPod was not an innovative product in and of itself. Years later, however, I realized the significance of ecosystem of which the iPod was a part. Apple had released iTunes (with technology purchased from  SoundJam MP ) and created the iTunes Store for finding and downloading music. Unlike Napster , it was a safe and legal way of distributing and acquiring music. The prior way of playing

Interaction Design: the Neglected Skill

Your product development organization has a big, gaping hole in it. (Be prepared to feel defensive as you continue reading.) One of the most important roles in product development is the role of interaction designer. An interaction designer designs how the users will interact with the product and conceptualize the tasks they perform. He decides whether, for example, the user interface will be command driven, object oriented (clicking on objects then specifying what to do with them), or wizard based. The interaction designer decides the individual steps in the use cases. Every company has one or more people that play the interaction designer role. Usually, those people have little or no expertise in interaction design. Sadly, they typically don't even realize how unqualified they are. Let's see who typically plays the role at companies. Engineer . An engineer is an expert on building what is designed. Yes, an engineer may know how to design the internal structure of the hardw